I second the "gas wrench" method. Start off with a simple propane torch, then move to MAPP gas, then finally, the Oxy-Acetylene (trying your luck after each).

Applying the aforementioned "spray" while the fitting is warm can often help it to penetrate. (Be careful it's not too hot when you spray, or you may have a fire! Be sure the Home Owner's insurance is up to date!)

I had a similar episode with my 300 Tdi crank pulley. I used a 24" breaker bar and jumped on it with all my weight (plus the weight of the beer in my hand) and it still wouldn't move. Fast forward four hours later and the Oxy-Acetylene heated bolt finally broke free after being heated cherry red and the full wrath of my rage was applied to the 24" breaker bar. I have a scar for life from the tiny radiator shroud stud that took a sizable chunk of my forearm for my trouble...

The manual states this should be tightened to 80-some odd ft/lb AND THEN turned 90 degrees! This is an insane amount of torque, equal to about 2.5 times the total available torque of the engine! I just don't get Land-Rover sometimes...